Ford F-150 Milage always the same
Okay so I drove my truck across the country from
point A I was getting 19 miles to the gallon on the
highway. Throughout the states my milage dropped
significantly to 10 miles to the gallon, and has risen
to 11.6 miles to the gallon now. Doesn’t matter if
I’m in town or highway. I could be going 90 with a
huge load in my truck or going 55 with nothing at all
and it stays the same. The oil is changed my air
filter is clean I’ve tried gas from several different
places. I’ve used injector cleaner tried premium gas
for a while and no change.
Try using the old pencil and paper method of calculating MPG's, and see if there is a significant change. Make sure transmission is not in the tow/haul mode. Transmission is electronic. Has it been serviced? You're over 100K miles. Fill the tank with gas and reset the trip counter to zero.
So even if it is in tow/haul more there still isn’t any change. And I’ve tried the old school method of mileage it’s pretty accurate.
Rich fuel mixture would be a cause, but you would probably get a check engine light and notice other performance issues. Could you 6R80 transmission be the cause. It's electronic. If a servo is defective it may not be shifting into the proper gear for best mileage. Probably a good idea to have a technician do a live date analysis while driving to see if the problem is there.